The ultrastructure and cytochemistry of exocrine secretory cells are being studied. Emphasis is being placed upon the basic mechanisms of secretion, with particular attention directed toward the role of the Golgi apparatus and lysosomes in these phenomena. The rat parotid and exorbital lacrimal glands are the primary focus of our investigations. However, other glands including the submandibular, sublingual, and lingual salivary glands, liver, pancreas, and intestinal glands are frequently utilized for comparative studies or to take advantage of particular structural or cytochemical characteristics. Other species, including mice, hamsters, guinea pigs, and monkeys, are also occasionally used. Five individual areas of investigation are currently underway. These are 1) the role of the Golgi apparatus and GERL in the formation of secretory granules in resting and stimulated glandular cells: 2) the function of the lysosomal system in degradation of secretory material and formation of crystalloids in animals treated with the amino acid analog DL-ethionine; 3) the effects of antimicrotubular agents such as vinblastine and colchicine, on the structure and function of glandular cells; 4) the cytochemistry of the Golgi apparatus and lysosomes of rat incisor ameloblasts; and 5) the structure, cytochemistry, and distribution of peroxisomes in various tissues.